The present invention relates to a damper disc used as a clutch disc of an automobile and others, and particularly, to a damper disc including stepped damping characteristics.
Conventionally, a disc including a stepped characteristic requires springs, of which number is at least same as a number of steps or stages in the damping characteristics. Particularly, if it is required to provide a sufficiently strong maximum rigidity against relative torsion or twist of input and output members, it is necessary to provide springs more than number of the operation stages. For example, if the disc is required to operate at four damping stages, i.e., soft, medium soft, medium hard, and hard stages, it is usually necessary to provide six or more sets of the springs in the disc. Therefore, many openings for the springs should be formed in a flange of a splined hub. Particularly, in the disc having a large maximum torsion angle, the disc should be provided with the long and wide openings and recesses for the springs and stopper pins, and thus, lengths between the adjacent openings and recesses become short, resulting in a weak strength of the flange.
Further in the conventional structures, the spring or springs for the first, i.e., weak, torsion operation are adapted to be compressed through the whole torsion area, i.e., until a torsion angle increases to a maximum value, so that a compressed length of the first spring becomes large, and thus, the stress thereof also becomes extremely large. Therefore, it is hard to maintain a sufficient strength in the first spring.